Character Set.

The programs generated by Lex handle character I/O only through the routines input, output, and unput. Thus the character representation provided in these routines is accepted by Lex and employed to return values in yytext. For internal use a character is represented as a small integer which, if the standard library is used, has a value equal to the integer value of the bit pattern representing the character on the host computer. Normally, the letter a is represented as the same form as the character constant 'a' . If this interpretation is changed, by providing I/O routines which translate the characters, Lex must be told about it, by giving a translation table. This table must be in the definitions section, and must be bracketed by lines containing only ``%T''. The table contains lines of the form

{integer} {character string}
which indicate the value associated with each character. Thus the next example

 1	Aa
 2	Bb
26	Zz
27	\n
28	+
29	-
30	0
31	1
39	9

Sample character table.

maps the lower and upper case letters together into the integers 1 through 26, newline into 27, + and - into 28 and 29, and the digits into 30 through 39. Note the escape for newline. If a table is supplied, every character that is to appear either in the rules or in any valid input must be included in the table. No character may be assigned the number 0, and no character may be assigned a bigger number than the size of the hardware character set.